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Advanced Geotechnical Engineering Dr.-Ing. B.V.S. Viswanadham Professor, Department of Civil Engineering Indian Institute of Technology Bombay Powai, Mumbai- 400 076, INDIA Website: www.civil.iitb.ac.in/~viswam Email: viswam@civil.iitb.ac.in
Course Outline Origin and the nature of soils as engineering materials; Soil classification schemes; Clay mineralogy Soil compaction; Soil-water interaction; Permeability and Seepage Consolidation behaviour of the soil and Methods for accelerating consolidation of the soil. The stress-strain-strength response of soils, Earth retaining structures and stability analysis of slopes Buried structures, and Geotechnical physical modelling
S.No. Module Contents 1. Soil composition and soil structure Soil formation; Types of soils and their characteristics; Particle sizes and shapes; their impact on engineering properties; Soil structure; Clay mineralogy; Soil-airwater interaction; Consistency; Soil compaction; Concept of effective stress.
S.No. Module Contents 2. Permeability and Seepage Permeability; Seepage force and effective stress during seepage; Laplace equations of fluid flow for 1-D, 2-D and 3D seepage, Flow nets, Anisotropic and non-homogeneous medium, Confined and Unconfined seepage.
S.No. Module Contents 3. Compressibility and Consolidation Stresses in soil from surface loads; Terzagahi s 1-D consolidation theory; Application in different boundary conditions; Ramp loading; Determination of Coefficient of consolidation c v ; Normally and Overconsolidated soils; Compression curves; Secondary consolidation; Radial consolidation; Settlement of compressible soil layers and Methods for accelerating consolidation settlements.
S.No. Module Contents 4. Stress-strain relationship and Shear strength of soils Stress state, Mohr s circle analysis and Pole, Principal stress space, Stress paths in p-q space; Mohr-coulomb failure criteria and its limitations, correlation with p-q space; Stressstrain behaviour: Isotropic compression and pressure dependency, confined compression, large stress compression, Definition of failure, Interlocking concept and its interpretations, Drainage conditions; Triaxial behaviour, stress state and analysis of UC, UU, CU, CD, and other special tests, Stress paths in triaxial and octahedral plane; Elastic modulus from triaxial tests.
S.No. Module Contents 5. Earth retaining structures 6. Stability of Slopes Earth pressures; Stress changes in soil near retaining walls; Earth pressure theories- estimation of earth pressures-drained and undrained loading. Stability analysis of a slope and finding critical slip surface; Sudden Draw down condition, effective stress and total stress analysis; Seismic displacements in marginally stable slopes; Reliability based design of slopes, Methods for enhancing stability of unstable slopes.
S.No. Module Contents 7. Buried Structures Load on Pipes, Marston s load theory for rigid and flexible pipes, Trench and Projection conditions, minimum cover, Pipe floatation and Liquefaction. 8. Geotechnical Physical Modeling Physical modeling methods; Application of centrifuge modeling and its relevance to geotechnical engineering; Centrifuge modeling of geotechnical structures.
Geotechnical engineering is the branch of Civil Engineering concerned with the engineering behaviour of earth materials. Geotechnical engineering uses principles of *Soil Mechanics and **Rock Mechanics to investigate subsurface conditions and materials *Soil Mechanics is the branch of science that deals with the study of the physical properties of soil and the behaviour of soil mass subjected to various types of forces. **Rock mechanics is the theoretical and applied science of the mechanical behaviour of rock and rock masses
Natural slope Cut slope Embankment dam Building foundation Examples of geotechnical engineering construction
Road embankment Geosynthetic Reinforced wall Supported excavation Tunnel Buried pipe Building on pile foundation Examples of geotechnical engineering construction
Conventional/Bioreactor landfills Ash Ash Compacted ash Compacted ash Heterogeneous Municipal Solid Waste Examples of geotechnical engineering construction
Sea wall Construction on soft soil Windmill foundation Examples of geotechnical engineering construction Offshore foundation
Typical geotechnical failures Expansive soil subgrade Mud pumping Landslide Landfill failure Slope failure Track subsidence
Geotechnical Engineering is simply the branch of engineering that deals with structures built of, or in, natural soils and rocks. This subject requires knowledge of strength and stiffness of soils and rocks, methods of analyses of structures and hydraulics of ground water flow.
Course Context An understanding of the engineering behaviour of the ground and the interaction between the ground and any structures built in or on the ground is essential for all Civil Engineers.
According to Karl Terzaghi (1883-1963): Unfortunately, soils are made by nature and not by man, and the products of nature are always complex As soon as we pass from steel and concrete to earth, the omnipotence of theory ceases to exist. Natural soil is never uniform. Its properties change from point to point while our knowledge of its properties are limited to those few spots at which the samples have been collected. In soil mechanics the accuracy of computed results never exceeds that of a crude estimate, and the principal function of theory consists in teaching us what and how to observe in the field.
Selected References Atkinson, J. (2007). The mechanics of soils and foundations. Taylor & Francis, London and New York, Second Edition. Aysen, A. (2005). Soil Mechanics: Basic Concepts and Engineering Applications, Taylor & Francis, London and New York, First Edition. Craig, R.F. (2004). Craig s Soil Mechanics, Spon Press Taylor & Francis, London and New York, Seventh Edition. Das, B.M. (2008). Advanced Soil Mechanics. Taylor & Francis, London and New York, Third Edition.
Selected References Fang, H-Y., and Daniels, J.L. (2006). Introductory Geotechnical Engineering: an Environmental Perspective. Taylor & Francis, London and New York, First Edition. Fredlund, D.G., and Rahardjo, H. (1993). Soil mechanics for unsaturated soils, John Wiley & Sons, New York, First Edition. Holtz, R.D., and Kovacs, W.D. (1981). An introduction to geotechnical engineering, Prentice Hall, New Jersey, Kaniraj, S.R. (2008). The mechanics of soils and foundations, Tata McGraw-Hill Publishing Company Ltd., New Delhi, Tenth Reprint.
Selected References McCarthy, D.F. (2007). Essentials of Soil Mechanics and Foundations: Basic Geotechnics, Pearson Prentice Hall, New Jersey, Ohio, Seventh Edition. Parry, R.H.G. (2004). Mohr circles, stress paths and Geotechnics. Spon Press Taylor & Francis, London and New York, Second Edition. Wood, D.M. (2004). Geotechnical Modelling, Spon Press Taylor & Francis, London and New York, First Edition.
Rock: The source of soils Most of the nonroganic materials that are identified as soil originated from rock as the parent material. The rocks that form the earth s surface are classified as to origin as: - Igneous - Sedimentary - Metamorphic
Igneous Rocks are those formed directly from the molten state of magma. The molten magma that cooled rapidly at or near earths surface are called extrusive or volcanic type rocks. Eg. Basalts, Rhyolites and Andesites. If the molten rock cools very slowly, the different materials segregate into large crystals forming a coarse-grained or granular structure (Trapped at deeper depths) Intrusive or plutonic type, Eg. Granite (which consists of quartz and feldspar), Syerites, and Gabbros Because of high silica content these rocks are classified as ACIDIC Decomposes to predominantly sandy or gravel with little clay. (Good construction materials!) Rocks whose minerals contain Fe, Mg, Ca or Na but little silica such as the Gabbros, Diabases, Basalts are classified as BASIC
Igneous Rocks When the solution of magma is cooled very very rapidly the minerals do not separate into crystals but solidify as amorphous vitreous rock. Such as, Volcanic Scoria, Pumice, and Obsidan Rock types that are intermediate between acidic and basic include the Trachytes, Diorites, and Andesites Easily break down into the fine-textured soils due to their mineral components. The clay portion of fine-textures soil is the result of primary rock minerals decomposing to form secondary minerals. Not small fragments of the parent rock minerals The properties and behaviour of clay soils are different from those of gravel, sand, and silt soils.
Sedimentary Rocks are formed from accumulated deposits of soil particles or remains of certain organisms that have become hardened by pressure or cemented by minerals. Cementing materials such as silica, Calcium Carbonate, iron oxides are abundant For E.g., Limestones, *Dolomites, Sandstone, Shale, Conglomerate and Breccia *Dolomite is referred to both the rock forming mineral CaMg(CO 3 ) 2 and sedimentary rock (recent name is Dolostone)
Sedimentary rocks Shales are predominantly formed from deposited clay and silt particles. - The degree of hardness = f ( the type of minerals, the bonding that developed, and the presence of foreign materials). - The hardness is mainly due to external pressures and particle bonds, not due to cementing minerals. - When exposed to environment (water or air), shales tend to expand or delaminate (the layers separate) - Break down of shale fragments of varying sizes Clay particle sizes
Sedimentary rocks Limestone is predominantly crystalline CaCO 3 (Calcite) formed under water. Limestone-Dolomite is referenced as Karst or Karstic terrain. Sinkholes/cavities can result due to solvable nature with ingredients present in ground water. Weathering of limestones predominantly finer size particles. Formation of sinkholes (Modified after: http://geoservicesltd.com/limestone sinkholes.html)
Metamorphic Rocks [Source: IR or SR] - results when any type of existing rock is subject to metamorphism, the change brought about by combinations of heat, pressure and plastic flow so that the original rock structure and mineral composition are changed. [ Plastic flow slow viscous movement and rearrangement within the rock mass due to external forces] Limestone MARBLE; Shale SLATE or PHYLLITE; Granite GNEISS; Sandstone QUARTZITE
Metamorphic Rocks Gneiss is a foliated rock with distinctive banding that results from the metamorphosis of granite. Distinction between Gneisses and Schists is not always clear Upon weathering Gneiss and Schist decompose to form silt-sand mixtures with mica. Soils from phyllites are more clayey and decomposition of quartzite produces sands and gravels.
Typical example of metamorphism
ROCKS (IGNEOUS, SEDIMENTARY, METAMORPHIC) WEATHERING (PHYSICAL/CHEMICAL) TRANSPORTED SOIL BOULDERS, GRAVEL, SAND, SILT AND CLAY
Rocks whose chief mineral is quartz minerals with high silica content, decomposes to predominantly sandy or gravelly soil with little clay. [Acidic rocks are light-coloured] Basic rocks decompose to the fine-textured silt and clay soils. - The clays are not small fragments of the original materials that existed in the parent rock [ result of primary rock minerals decomposing to form secondary minerals]
Major soil types based on particle size The major engineering categories of soil are gravel, sand, silt and clay Gravel and sands are considered coarse-grained soils (with large bulk particle sizes) Silt (very tiny particles of disintegrated rock) and clay particles are considered fine-grained soils because of their small particle sizes. - Clay soil is plastic (if it can be remolded without cracking/breaking) over a range of water content and silt soil possesses little or no plasticity. Particles larger than gravel are called cobbles or boulders
Soils can be grouped into two broad categories (depending on the method of deposition): Residual Formed from weathering of rock and remain at the location of their origin. [a material which may possess little mineralogical resemblance to the parent rock] Transported those materials that have been moved from their place of origin - by agencies like, gravity, water, glaciers, or man- either singularly or in combination
Characteristics of Residual soils are dependent on: Climatic conditions - humidity, temp., rainfall) Natural drainage pattern Form and extent of vegetation cover [A warm and humid climate is favourable to the formation of residual soils and nature of residual soil differs markedly at different depths below ground surface and constantly changes with time] - Soil deposits in Deccan Plateau
Transported Soils are classified according to the transporting agency and method of deposition: Alluvial transported in running water [rivers] Lacustrine deposited in quiet lakes Marine deposited in sea water Aeolin transported by wind Glacial by ice [Glaciation massive moving sheets of ice Colluvial deposited through action of landslide and slope wash
Examples of Transported soils: LOESS Wind blown deposit with very uniform fine silt particles (possesses slight cementation properties) Formed in Arid and Semi-Arid regions with yellowish light brown colour Tuff Fine-grained slightly cemented volcanic ash [by wind/water] Glacial till Heterogeneous mixture of boulders, gravel, sand, silt and clay [Hilly regions]
Examples of Transported soils: Varved Clay Alternate layers of silt and clay deposited in fresh water glacial lakes. - One band of silt and clay deposited each year [each layer is approx. 10 mm thk.] Marl Very fine grained soil of marine origin [impermeable, greenish colour] Peat A highly organic soil consisting almost entirely of vegetable matter in varying stages of decomposition, Fibrous, brown to black in colour and highly compressible
Major soil deposits: f( Ambience, Geography and Topography) Expansive High shrink-swell characteristics (attributed to the mineral) Colour- Black (presence of Fe, Mg and Ti) Marine Very soft and may contain organic matter Laterite Red in colour due to Fe 2 O 3 (Laterization- Leaching of Silica due to intense chemical weathering) Alluvial Alternate layers of Sand, Silt and Clay Desert Wind blown, Uniformly graded Glacial Boulder clay (all ranges of particle sizes)
Distribution of predominant Soil deposits In India Desert soils Expansive soil deposits Marine soil deposits
Constituents of the soil mass -Formation of soils from the weathering of the parent rock -Wide range of sizes of soil solids Behaviour of soil mass under stress is a function of material properties, such as: (i) size and shape of grains, (ii) gradation, (iii) mineralogical composition, (iv) arrangement of grain, (v) inter-particle forces, etc.) Material properties f(constituents of the soil mass)
Constituents of the soil mass Soil is a particulate material, which means that a soil mass consists of accumulation of individual particles that are bonded together by mechanical or attractive means, though not strongly as for rock. - Spaces in between solid particles Voids or pore space In soil (in most rock), voids exist between particles, and voids may be filled with a liquid, usually water or gas, usually air.
Actual soil bulk consisting of soil particles, water and air Air in irregular spaces between soil particles Water surrounding particles and at points of contact between particles, and filling small void spaces
Constituents of the soil mass Soil is inherently multiphase material (Generally consists of three phases) - Solid phase - Liquid phase - Gaseous phase It can also be TWO PHASE material: - With solid + Gaseous (DRY STATE) - With solid + Liquid (SATURATED STATE)
3 Phase system GAS LIQUID Idealization SOLIDS
Solid phase consists of: Primary rock forming minerals (Size > 2µm, Poor Reactivity, Prone to disintegration) Clay minerals (Basic materials that form the soil mass, Size < 2µm, High Reactivity) Cementing material (Carbonates) Organic matter (High water absorption, Compressible, unstable)
Liquid phase consists of: WATER DISSOLVED SALTS Pure water Polluted water Water soluble Water insoluble Water soluble- Chlorides, Sulphates, Bicarbonates (Not capable of binding solid grains)
Gaseous phase consists of: AIR GASES Air Solids 2 phase system; Dry soil Water Solids 2 phase system; Saturated soil
3 Phase system Volume Weight V a AIR W a = 0 = V V V w WATER W w V s SOLIDS W s V = V S +V W +V a W = W S + W W Partially Saturated Soil
3 Phase system Volume Weight V a AIR W a = 0 = V V V w WATER W w V s SOLIDS W s V = V S +V W +V a W = W S + W W Partially Saturated Soil
Self evaluation i) List the soil types included in coarse-grain category and the fine-grain category ii) Why there is a difference in behaviour of natural clays and other soil types such as sands and silts? iii) What does the term plastic mean in relation to clay soils? iv) What are laterites (or lateritic soils) and why are such soils considered in the category of requiring special consideration on construction projects? v) From any borehole data in your location, list soil type and rock types